The present invention relates to the field of pigmented coating materials. In particular, the present invention relates to pigment flakes having brilliant and highly reflective optical characteristics, to coating applications thereof, and to a method of making the pigment flakes using vapor deposition techniques to deposit a thin layer of colorant directly on a core material which is subsequently fractured to form discrete flakes.
Colorants are well known classes of chemicals which are used to color or modify the hue of a substrate. Various forms of colorants have been used throughout human history. The term colorant includes, but is not limited to, organic and inorganic pigments, dyes, and combinations thereof. Metals are considered inorganic pigments; however, pure metals and alloys are frequently considered separately. The Colour Index International: Fourth Edition Online (Colour Index) is an internationally recognized registry of colorants, and is published jointly by the British-based Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists. The Colour Index is found online at www.colour-index.org, and includes 800 color index classifications and a listing of thousands of pigment and dye products. The listings include chemical properties and manufacturers.
The fundamental difference between pigments and dyes is that dyes are soluble in the application medium while pigments are insoluble. Colorants, in general, are divided into appropriate hue groups, which include yellow, orange, red, violet, blue, green, brown and black in that order, additionally pigments further include the hue groups white and metals. Objects are colored if they selectively absorb and reflect incident light. Pure white reflects all light uniformly and pure black reflects no light. Pigments retain a crystal or particulate structure throughout the coloration process. Furthermore, pigments alter appearance by selective absorption and/or by scattering of light. Pigments are usually dispersed in vehicles or substrates for application, as for instance in the manufacture of inks, paints, plastics, or other polymeric materials. Dyes, on the other hand, are soluble, and the crystal structure of the chemical substance is typically destroyed, at least temporarily.
Pigmented coatings and pigment powders are well known. Pigment powders are composed of very small particles or flakes of organic or inorganic pigment. Particle shape is important in some applications. Needlelike particles apparently improve brushability and enhance adhesion, while platelike particles physically block out light and moisture thereby offering corrosion protection. A variety of particulate shapes are known, including needlelike, rodlike, spherical, cubic, small platelet and large platelet. Combinations of shapes may be present in single batches of pigment. Particle size is also an important consideration that influences the color strength, gloss, rheology, opacity and light fastness of pigment applications.
Pigmented coatings typically involve suspending a small amount of pigment powder in water or a volatile substance, applying the suspension to a substrate, and allowing the liquid in the suspension to evaporate thus covering the substrate with particles of pigment. U.S. Pat. No. 3,713,870 discloses a coating method for depositing metallic flakes on the surface of an object; the method involves suspending very thin, relatively small flakes in a volatile liquid, coating an object with the resulting suspension, and allowing the volatile liquid to evaporate resulting in the object having a thin, metallic coating held in place by intermolecular attraction. U.S. Pat. No. 4,003,872 describes a process whereby small flakes of metal and plastic particles are polished together to form a polished metal flake pigmented plastic powder product; upon application to a substrate, the plastic powder product is melted to form a smooth uniform film coating. Nearly all coatings require flakes of organic or inorganic pigment to provide the desired optical effect.
Generally, the amount of reflection a surface presents is directly proportional to the smoothness and regularity of the surface on the molecular level. Densely packed molecular surfaces, which are relatively unbroken having few apertures, breaks, depressions or prominences, are highly reflective. Light hitting a smooth and regular molecular surface reflects off the surface at highly uniform, discrete angles resulting in a brilliant and lustrous appearance analogous to smooth polished metals or mirrors. Light striking an irregular molecular surface is reflected at odd, nonuniform angles resulting in a dull appearance.
Most affordable pigments naturally have irregular shapes resulting in a dull, lusterless appearance. For example, the natural state of aluminum, an ingot, has a dull light-gray appearance. The molecules of aluminum naturally clump together in irregular patterns. A microscopic view would reveal jagged surfaces with crevices and protrusions. When aluminum is ground up and dispersed into a coating medium such as water or other solvent, and applied utilizing any conventional coating, printing or other technique, the resulting appearance is dull and gray. The natural states of nonmetallic inorganic and organic pigments are comparable. The appearances of other pigments in coating and printing applications having similar irregular shapes are the same. Carbon black, for example, has an irregular lumpy shape at the molecular level and a dull black appearance. When nonmetallic inorganic or organic pigments are fractured and utilized in coating, printing or other applications, the result is a flat nonreflective coloring.
Many techniques are utilized to improve the smoothness, gloss and brilliance of coatings containing pigmented powder. The first consideration is the smoothness and regularity of the article to be coated. Providing an initially smooth and regular surface is the first step in achieving a reflective, glossy coat. Other techniques involve grinding the pigment into very fine particles, integrating the particles into a coating composition, cross-linking the coating through energy infusion, and doctoring, calendering or embossing after the coating has been applied to the substrate. Additionally, extreme precision in the placement of pigment flakes in coating or printing applications may be used to assure that the pigment flakes present a smooth face so that the angles of reflection of the separate flakes are predominantly uniform. These techniques may be quite expensive and time consuming.
Dyes are inherently nonreflective. According to the Dyes and Toxicology Organization, which represents domestic dye manufacturers, dyes are defined as intensely colored or fluorescent organic substances which impart color to a substrate by selective absorption of light. To be reflective, dyes must be added to a reflective medium such as a glossy coating medium or the like.
Numerous methods have been developed to make fine thin flakes of metal for use as pigments. These metallic flakes have the disadvantage of bending, curling or breaking. Malformed metallic flakes have less than desirable optical qualities because they do not present a smooth surface. U.S. Pat. No. 4,321,087 issued to Levine et al. on Mar. 23, 1982 discloses a process for making metallic leafing pigments. The process therein involves a release coating continuously applied to at least one side of a carrier sheet. Metal vapor is condensed onto at least one surface of the release coating forming a thin metal film. The carrier sheet, the release coating and the thin metal film are then passed through a solvent system which releases most of the thin metal film into the solvent. The thin metal film is placed in a non-reactive liquid medium where it is fractured into finer pigment particles by vigorous stirring or ultrasonics The resulting metal flakes are concentrated and formulated into coating and printing compositions.
U.S. Pat. No. 5,718,753 b issued to Suzuki et al. on Feb. 17, 1998 describes colored metallic pigment flakes and the preparation thereof. The invention involves using a vacuum evaporation apparatus, which may have a vibrating unit, to produce metallic flakes having colored pigment evenly deposited on a metal core. Furthermore, the invention of Suzuki et al. describes a method for coloring polymeric materials en mass by contacting the particles of colored metallic pigment with polymeric material, incorporating the particles into the polymeric material, and utilizing the polymeric material as a coating composition. The colored metallic flakes still may become malformed reducing their reflective quality.
U.S. Pat. No. 5,895,524 issued to Dickson on Apr. 20, 1999 describes a method of making thin film metal particulates for use as paint pigments. The method involves immersing a metallized sheet of fluorinated ethylene propylene first in an aqueous base and then in an aqueous acid to loosen and release the metal. The metals are subsequently dislodged from the fluorinated ethylene propylene with one or more counter rotating cylindrical nylon bristle brushes, or with ultrasonic vibration alone or in combination with the brushes. Thin metal particulates are formed. The metallized sheet of fluorinated ethylene propylene with the proper thickness may be prepared by sputtering the metal onto 2 mil thick fluorinated ethylene propylene sheet stock. Suitable metals include germanium and aluminum. The invention of Dickson is useful only for producing pigment flakes of metals and not for nonmetal colorants.
U.S. Pat. No. 4,116,710 issued to Heikel on Sep. 26, 1978 discloses a method of making metallic particulates suitable for use in coating compositions. The method involves depositing a metal on a substrate by electroless, vapor (including vacuum evaporation), or sputter deposition methods. The metal deposit is subsequently removed from the substrate either by dissolution of the substrate or ultrasonic means to provide a plurality of distinct metal platelets suitable for use as pigment particles. The invention of Heikel cannot be used with nonmetallic colorants regardless of the type. Generally, inventions used to produce metallic platelets, or to metallize substrates, cannot be utilized with nonmetallic colorants.
U.S. Pat. Nos. 3,697,070 and 3,988,494 issued to McAdow, on Oct. 10, 1972 and Oct. 26, 1976 respectively, describes a metallizing coating composition which is formed by sandwiching a flat polished piece of metal, preferably aluminum, between two layers of insoluble resin. The metallizing coating composition is then broken up to create small planar flakes which are flat and reflect light over a greater area. The resulting metallic pigment powder can be used as a coating powder in a conventional manner. Any colorant used must form a thin sheet with a smooth polished surface; consequently, the invention of McAdow cannot be used with typical nonmetallic colorants.
Lamination is another common method that has been used for some time. Aluminum, for example, can be calendered into a foil which is molecularly smooth and regular. The constant and uniform pressure of the calendering smooths the irregularities found in naturally occurring aluminum producing a smooth reflective surface. The resulting aluminum can subsequently be laminated to an object creating a bright, reflective surface.
Physical and chemical vapor deposition processes are well known. These processes are used to deposit molecules on a substrate. These processes may be used for decorative purposes to deposit a colorant on a substrate. Chemical vapor deposition is not typically used for decorative purposes but is used widely in the microchip industry. Numerous techniques are utilized which deposits molecules via physical vapor deposition. All of these techniques involve forming a vapor of the molecules to be deposited on a substrate. Some methods involve vacuum deposition processes, which rely on lowered pressure to propel the vapor onto the substrate. Vacuum evaporation (also known as vacuum metallizing when metals are involved), sputter deposition, arc vapor deposition, and ion plating are common methods for physical vacuum deposition. All vapor deposition processes have the disadvantage that they coat the substrate, or the exposed part of the substrate, with the evaporated colorant molecules. They are not useful in printing, painting or other applications requiring discrete use of the colorant so applied.
Vacuum metallizing is a common coating technique. Various methods of vacuum metallizing can accomplish even higher degrees of gloss than metallic laminations. The principle behind metallizing is to provide conditions, such as heat and pressure, under which aluminum, or other suitable metals, are vaporized. Nonmetallic organic and inorganic pigments may be vacuum deposited on a substrate via vacuum evaporation. The vapor of metal or other pigment is brought into contact with the surface of an object forming a coating thereon. The result is a very thin, very regular deposit of colorant on the surface of the object. This coating is only a few molecules thick, and has a brilliant and highly reflective surface. The thickness of the coating is readily controlled; however, the initial surface of the object must be sufficiently smooth to allow uniform reflection to achieve optimum results. The thinness of the coating will not fill any crevices or irregularities already present on the surface of the substrate.
Vacuum evaporation, or metallization, is not practical for use directly on paper or other objects having an irregular, rough surface. Paper, for example, must be pre-coated and pre-treated to provide the smooth, regular surface needed for metallization. Metallization of various films, including polyester, is practical, however, the film must be subsequently laminated on paper or paper-board for many artistic uses. Lamination of paper results in added costs and an extra thick layer of film, which is both unnecessary and undesirable.
Sputter deposition can be used with elements, alloys or compounds. The process can be performed in a vacuum or low-pressure gas. It can also be performed under higher atmospheric pressures by using thermalized particles. Sputter deposition is precise enough to make a line or perhaps letters. It has the disadvantage of being expensive and may require a great deal of heat. It is not useful for decorative printing or coating applications.
Arc vapor deposition is a coating method which requires the vaporization of an anode or a cathode. The substrate upon which the vapor is deposited is the opposite vapor source and serves as the cathode or anode. Clearly, this method has the disadvantage of being useful for electrically conductive materials only. This method is similar to electroplating.
Ion plating can be done in a plasma environment where ions are extracted from the plasma and bombarded onto the substrate. Another version of ion plating, referred to as ion beam assisted deposition, is done in a vacuum environment where the ions for bombardment are formed in a separate ion gun. Atomic packing near the surface of the growing film can be densified by concurrent ion bombardment (known as atomic peening) by the ion plating process. This method is not used for decorative purposes as it requires the control of many processing variables, and is typically used to deposit hard coatings of compound materials.
Plasma-enhanced chemical vapor deposition is a chemical deposition method which reduces the decomposition of a chemical-vapor precursor species that contains the material to be deposited. This method may be used to deposit a single layer of crystals on a substrate. Many elements, alloys, and glassy and compound materials can be deposited in this way. This method is typically used in semi-conductor processing and not for decorative purposes.
Hybrid vacuum deposition processes are frequently used. These processes are when two deposition techniques are used either concurrently or sequentially. The same limits are applicable to the combination of two or more techniques as to each individual technique.
Electroplating is another technique commonly used to coat the surface of an object. Electroplating is the process of coating an object with a metal using an electric current. The plating metal may be transferred to conductive surfaces, typically metals, or to nonconductive surfaces, such as plastics, wood or leather, only after the latter have been rendered conductive by such processes as coating with graphite, conductive lacquer, electroless plate, or a vaporized coating. Obviously, electroplating is unsatisfactory for use on many objects, especially paper or paperboard. Likewise, the cost and added steps involved in electroplating make it undesirable. Furthermore, electroplating may only be used with conductive materials, and is completely useless for coating objects with nonconductive colorants.
Transfer metallization is another technique which involves vacuum metallizing a specially prepared plastic film, laminating the metallized film onto another surface, and then stripping off the unwanted film. This technique reduces the costs of using the paper with the film but increases the manufacturing costs. The manufacturer must add a stripping operation to the process, and must discard, or recycle, the unwanted film in an environmentally sound procedure.
Glazing is another method used to coat objects. U.S. Pat. No. 5,358,669 issued to Demiryont et al., on Oct. 25, 1994, discloses a process for preparing plastic composite glazings which involves depositing a metal film on one surface of a plastic sheet, heating the metal film and plastic sheet to a temperature above the plastic set temperature, and deforming/mixing the plastic sheet and metal to form a plastic matrix having metal particles homogeneously dispersed therein.
Other methods have been developed to integrate metals into polymers for a variety of purposes including forming conductive polymers, and protective magnetic films. U.S. Pat. No. 5,418,056 issued to Noguchi et al. on May 23, 1995 discloses a polymer composite which includes a thermoplastic plastic polymer with a fine grain metal or metal oxide dispersed therein. A method of making the polymer composite is also disclosed. The method involves melting a polymer material, rapidly solidifying the melted polymer to form a thermodynamically non-equilibrated polymer layer, sticking a metal layer to the polymer layer, and relaxing the polymer layer until equilibrium is reached thereby dispersing fine grains (1000 nm or less) of the metal into the polymer. Alternatively, the steps forming a thermodynamically non-equilibrated polymer layer may be carried out by vacuum depositing the polymer on a ground via vacuum evaporation. Metal oxides may be substituted for the metals. The invention of Noguchi et al. may not be utilized with non-metallic pigments, and does not create a shinny metallic pigment but produces a conductive polymer. Similar polymers containing metals do not have the optical qualities desirable for pigment powders or coatings.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus, a pigment flake solving the aforementioned problems is desired.
The present invention is a method of making pigment flakes having unique qualities. These qualities include highly reflective metallic pigment flakes and unique appearing nonmetallic pigment flakes. The pigment flakes are composed of a core having a colorant deposited evenly on at least one surface thereof, preferably both. The core/colorant combination is subsequently fractured forming pigment flakes which are suitable for use in coating and printing applications.
Colorants used in the present invention are preferably organic or inorganic pigments, dyes, or combinations thereof. The core may be made of any suitable material including natural and synthetic polymers, resin and suitable combinations thereof. The core may be in any suitable form such as a continuous film, thin wires, thicker sheets, ropes, or straws.
The method for making pigment flakes according to the current invention involves providing a core of suitable material and form, depositing a fine layer of colorant molecules on the surface of the core, and fracturing the core/colorant combination to form pigment flakes. The core/colorant combination may be fractured into pigment flakes in the shape of needles, rods, spheres, cubes, small platelets, large platelets, or combinations thereof. The resulting pigment flakes may be substituted for conventional pigment powder and resinated pigments in any coating, printing or similar application. Furthermore, the pigment flakes, of the current invention, may be substituted for conventional pigment powders in any application which utilizes pigment powders provided the physical parameters, such as temperature and solvent, are appropriate.
An object of the invention is to provide pigment flakes which may be integrated into coating materials to yield brilliant, unique and light reflective surfaces. The pigment flakes of the current invention may be used in any manner in which conventional pigments are used. They are suitable for use in liquid dispersions, emulsions, pastes, powder and other forms.
It is another object of the invention to provide pigment flakes which are molecularly smooth and uniform so that light reflects off the surface at highly uniform and discreet angles. To this end, a combination of organic pigments, inorganic pigments and dyes may be used to make a single type of pigment flake having unique characteristics. Likewise, different types of pigment flakes of the current invention may be mixed in a single application to produce unique, aesthetically pleasing, optical qualities.
It is a further object of the invention to provide pigment flakes which can be integrated into coating and printing applications for use on a large variety of surfaces. Such surfaces include, but are not limited to, wood, metal, composites, plastics, paper, and paper-board. These pigment flakes may be used in paints, inks, and in any other medium which utilizes conventional pigments.
Another object of the invention is to eliminate unnecessary waste by reducing the energy and materials needed to coat substrates with a metallic coat. The invention produces less excess materials which must be discarded. Also, since the invention may be utilized directly as a pigment and/or as a binder vehicle in coating and printing applications to form highly reflective and shiny surfaces, far fewer steps are required to create the desired effect. Furthermore, less damage to the pigment flakes occurs because of less handling.
Additionally, the amount of colorant deposited by vapor deposition, and similar methods, is a tiny fraction of the amount used in conventional coatings, laminates, and the like. The cost of pigments often represents a large percentage of the total cost of conventional methods. The present invention is considerably less expensive yet yields similar, or superior, brilliance and light reflectivity. Also, the use of dyes in the pigment flakes of the present invention increases the number of available colors (hues), and broadens the potential optical effects attainable.
An object of the invention is to provide a method for manufacturing pigment flakes continuously with no interruptions except machine maintenance. The pigment flakes can be formulated for particular attributes permitting printing or coating applications to be tailored accordingly. The integration of the present invention into a coating material can be processed in line with the making of the pigment flakes. Alternatively, the making of the flakes can be a complete operation so that the pigment flakes can be sold as a pigment powder for integration into a coating at a later time, or the pigment flakes can be used directly as a pigment resin.
The pigment flakes of the present invention and the method for making the pigment flakes are unique in the field of colorants. The typical prior art which involves coating a polymer with metal then removing the polymer to form sheets of metal, or sandwiching the metal between polymer films, teaches in the opposite direction of the present invention.